Exclude Jinja >= 3.1 in the sphinx docs documentation.

Issue: readthedocs/readthedocs.org#9038

cmake/python.cmake

@@ -98,7 +98,7 @@ function(install_sphinx_package TARGET_NAME VENV_TARGET)
             ${CMAKE_COMMAND} -E touch ${INSTALL_TIMESTAMP}
         COMMAND
             # TODO install only necessary packages (e.g. breathe is not needed by python docs generator)
-            ${INSTALL_VENV_EXECUTABLE} -m pip install sphinx==3.3.1 sphinx_rtd_theme==0.5.0 six breathe docutils==0.16
+            ${INSTALL_VENV_EXECUTABLE} -m pip install Jinja2<3.1 sphinx==3.3.1 sphinx_rtd_theme==0.5.0 six breathe docutils==0.16
             "git+https://github.com/pjarosik/matlabdomain@master#egg=sphinxcontrib-matlabdomain"
         DEPENDS
             ${VENV_TARGET}